Add SqlFunc.IsNull

Src/Asp.Net/SqlServerTest/Demos/1_Query.cs

@@ -433,6 +433,7 @@ namespace OrmTest.Demo
         {
             var db = GetInstance();
             var t1 = db.Queryable<Student>().Where(it => SqlFunc.ToLower(it.Name) == SqlFunc.ToLower("JACK")).ToList();
+            var t2 = db.Queryable<Student>().Where(it => SqlFunc.IsNull(it.Name,"nullvalue")=="nullvalue").ToList();
             //SELECT [Id],[SchoolId],[Name],[CreateTime] FROM [Student]  WHERE ((LOWER([Name])) = (LOWER(@MethodConst0)) )
 
             /***More Functions***/

Src/Asp.Net/SqlSugar/ExpressionsToSql/DbMethods/DefaultDbMethod.cs

@@ -271,6 +271,13 @@ namespace SqlSugar
             return string.Format("{0}", parameter1.MemberValue);
         }
 
+        public virtual string IsNull(MethodCallExpressionModel model)
+        {
+            var parameter = model.Args[0];
+            var parameter1 = model.Args[1];
+            return string.Format("ISNULL({0},{1})",parameter.MemberName,parameter1.MemberName);
+        }
+
         public virtual string True()
         {
             return "( 1 = 1 ) ";

Src/Asp.Net/SqlSugar/ExpressionsToSql/DbMethods/IDbMethods.cs

@@ -48,6 +48,7 @@ namespace SqlSugar
         string AggregateMax(MethodCallExpressionModel model);
         string AggregateCount(MethodCallExpressionModel model);
         string MappingColumn(MethodCallExpressionModel model);
+        string IsNull(MethodCallExpressionModel model);
         string GetSelfAndAutoFill(string shortName,bool isSingle);
         string True();
         string False();

Src/Asp.Net/SqlSugar/ExpressionsToSql/DbMethods/SqlFunc.cs

@@ -67,6 +67,7 @@ namespace SqlSugar
         public static int DateValue(DateTime date, DateType dataType) { throw new NotSupportedException("Can only be used in expressions"); }
         public static bool Between(object value, object start, object end) { throw new NotSupportedException("Can only be used in expressions"); }
         public static TResult IIF<TResult>(bool Expression, TResult thenValue, TResult elseValue) { throw new NotSupportedException("Can only be used in expressions"); }
+        public static TResult IsNull<TResult>(TResult thisValue, TResult ifNullValue) { throw new NotSupportedException("Can only be used in expressions"); }
         public static int ToInt32(object value) { return value.ObjToInt(); }
         public static long ToInt64(object value) { return Convert.ToInt64(value); }
         /// <summary>

Src/Asp.Net/SqlSugar/ExpressionsToSql/ResolveItems/MethodCallExpressionResolve.cs

@@ -407,6 +407,8 @@ namespace SqlSugar
                     Check.Exception(!isValid, "SqlFunc.MappingColumn parameters error, The property name on the left, string value on the right");
                     this.Context.Parameters.RemoveAll(it => it.ParameterName == model.Args[1].MemberName.ObjToString());
                     return mappingColumnResult;
+                case "IsNull":
+                    return this.Context.DbMehtods.IsNull(model);
                 case "GetSelfAndAutoFill":
                     this.Context.Parameters.RemoveAll(it => it.ParameterName == model.Args[0].MemberName.ObjToString());
                     return this.Context.DbMehtods.GetSelfAndAutoFill(model.Args[0].MemberValue.ObjToString(), this.Context.IsSingle);